An electronic component such as flip chip having bumps is mounted by bonding the bumps, which protrude from the body of the electronic component, with electrodes formed on a substrate. The substrate on which the electronic component is mounted suffers, depending on the application, from heating cycles, namely, repeated large changes of temperature. In general, the electronic component having bumps is an IC chip whose base material is a silicon single crystal. On the other hand, for the substrate on which the electronic component is mounted, resin or ceramic is generally utilized. Since there is large difference of the coefficient of linear thermal expansion between the silicon single crystal and the resin or the ceramic, when the mounted component is used under condition of large change of temperature, repeated stress acts on the bonded portions of the bumps of the electronic component and the electrodes of the substrate or on the bonded portions of the electronic component and the bumps, which may result in the breaking of the bonded portions.
In the following, an explanation on a conventional mounting structure of an electronic component having bumps is described referring to illustrations. FIG. 5 is a cross sectional view showing the conventional mounting structure of an electronic component having bumps. In FIG. 5, electrodes 2 formed on a substrate 1 are bonded with the bumps 4 of an electronic component 3 by soldering. Between the substrate 1 and the electronic component 3, under-fill resin 5 is formed. The under-fill resin 5 is for protecting the bonded portions of bumps 4 and electrodes 2 from water or the like and for decreasing the stress caused by the heat cycle described above.
From the standpoint of decreasing the stress, the coefficient of linear thermal expansion of the under-fill resin 5 formed between the electronic component 3 and the substrate 1 is desired to be an intermediate value between those of the electronic component and the substrate. However, the coefficient of linear thermal expansion of epoxy resin used in general for under-fill resin is much larger than those of a silicon single crystal used for the electronic component 3 and ceramic used for the substrate 1. At present, no resin is available, in actual use, for under-fill resin which meets the above-described condition.
Therefore, in the conventional mounting structure of the electronic component having bumps, the under-fill resin does not work effectively for decreasing the stress caused by the heat cycles, so that there is a problem that the reliability of the mounting structure is not satisfactory.